If this is a open breech plug the best way to clean them is with Q-tips and a good solvent. Then take that to an air compressor and blow air through it both ways. This will dry it and clean the channel. Hold it up and away from your eye to a window. You should be able to see through it. You will see a very small tunnel of light.

Also if you wash them in soap and water, I like to plug the end and fill it with isopropyl alcohol. Hold the alcohol in it for a while and then dump it. This helps any hidden water in it gets removed..

If it is a closed style breech plug, I water wash it, and wipe it all off nice and clean. Again pour some alcohol through it. And then hit it with an air compressor.